java - Swing Jcombobox 将第一个元素设置为默认选中

Question

    String[] bookArray={"a","b","c"};
    JComboBox bookComboBox = new JComboBox(bookArray);
    bookComboBox.setSelectedIndex(0);
    bookComboBox.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            JComboBox cb= (JComboBox) e.getSource();
            bookNameSelected=(String) cb.getSelectedItem();
            System.out.println("book name selected:"+bookNameSelected);
            }
    });

下拉列表的第一个元素显示为默认值，但如果用户未选择任何值，则不会作为默认选择值传递。

Answer 1

在ActionListener注册之后移动bookComboBox.setSelectedIndex(0);，这允许触发ActionListener并设置bookNameSelected

String[] bookArray = {"a", "b", "c"};
JComboBox bookComboBox = new JComboBox(bookArray);
bookComboBox.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent e) {
        JComboBox cb = (JComboBox) e.getSource();
        bookNameSelected = (String) cb.getSelectedItem();
        System.out.println("book name selected:" + bookNameSelected);
    }
});
bookComboBox.setSelectedIndex(0);